Polymeric materials, such as plastics, have been developed as alternatives and replacements for silica based inorganic glass in applications such as, optical lenses, fiber optics, windows and automotive, nautical and aviation transparencies. These polymeric materials can provide advantages relative to glass, including, shatter resistance, lighter weight for a given application, ease of molding and ease of dying. Representative examples of such polymeric materials include, poly(methyl methacrylate), polycarbonate and poly(diethylene glycol bis(allylcarbonate)).
The refractive indices of many polymeric materials are generally lower than that of high index glass. For example, the refractive index of poly(diethylene glycol bis(allylcarbonate)) is about 1.50, compared to that of high index glass, which can range, for example, from 1.60 to 1.80. When fabricating lenses to correct a given degree of visual defect, for example, a correction for myopia, the use of a polymeric material having a lower refractive index will require a thicker lens relative to a material having a higher refractive index, such as high index glass. If the degree of correction required is substantial, such as in the case of severe myopia, a lens fabricated from a low index polymeric material can become so thick as to negate any benefit of reduction in weight, as compared to an equivalent degree of correction provided by a higher refractive index lens, such as a high refractive index glass lens. In addition, thicker optical lenses generally are not aesthetically desirable.
Polymeric materials prepared from the polymerization of monomers containing aromatic rings typically have high refractive indices. Shaped articles, such as optical lenses, prepared from such high index polyaromatic materials, however, generally have lower ABBE numbers (also known as nu-values). Lower ABBE numbers are indicative of an increasing level of chromatic dispersion, which is typically manifested as an optical distortion at or near the rim of the lens. As such, optical materials having lower ABBE numbers are generally less desirable.
Polymeric materials having a combination of high refractive indices, such as at least 1.57, and low levels of chromatic dispersion (e.g., having ABBE numbers of at least 30), can be prepared from monomers containing certain heteroatoms, such as sulfur atoms. Such polymerizable compositions when polymerized with thermally activated catalysts can, however, undergo erratic and/or excessive rates of polymerization, which result in defects in the resulting polymerizates, such as visible lines, surface defects (e.g., dimples and/or craters), and/or cracks or fissures, within the body and/or through the surface of the polymerizate.
It would be desirable to develop polymerizable compositions that provide desirable optical properties, such as a combination of high refractive index and reduced chromatic dispersion. It would be further desirable that such newly developed polymerizable compositions are not subject to erratic and/or excessive rates of polymerization, and polymerizates prepared therefrom are free of defects resulting from such uncontrolled polymerization.